This invention relates to a single overhead cam multi-valve engine and more particularly to an improved valve orientation, valve operating mechanism and induction system for such an engine.
It has been recognized that the performance of an internal combustion engine can be improved by increasing the number of intake valves for the engine. The use of two intake valves for high performance engine has been widely accepted. Although an even greater number of intake valves may improve induction efficiency, there are some difficulties in providing more than two intake valves for a given cylinder. Specifically, as the number of intake valves is increased beyond two, it is difficult to obtain a compact combustion chamber and, accordingly, a high compression ratio. In addition, the combustion-chamber configuration may be less than optimum if more than two intake valves are employed. That is, it is difficult to obtain the desired spherical combustion chamber configuration if more than two intake valves are employed. Furthermore, if more than two intake valves are employed the combustion chamber, particularly in the area where the valves seats are adjacent to each other can become irregular.
It is, therefore, a principle object of this invention to provide an improved valve arrangement and cylinder head for an internal combustion engine in which at least three intake valves may be employed.
It is a further object to this invention to provide a cylinder head arrangement for an internal combustion engine having at least three intake valves that will have a smooth combustion chamber configuration.
It is a further object of this invention to provide an improved arrangement for the cylinder head of an internal combustion engine that permits the use of three or more intake valves while maintaining a compact combustion chamber and one having a smooth configuration.
In conjunction with the use of two or more valves, it has been found that the combustion chamber configuration can be better made if the valves are disposed at different acute angles to a plane containing the axis of the cylinder bore. Where this is done, however, in order to simplify the operation of the valves, it has been proposed to employ valves having different length stems for the same purpose. This gives rise to obvious disadvantages both in assembly and in servicing the engine plus it requires the inventorying of a greater number of parts.
It is, therefore, a further object of this invention to provide a cylinder head arrangement for an internal combustion engine employing plural valves that are angularly disposed but which all have the same length stems.
In addition to the difficulties in connection with the combustion chamber configuration with the use of multiple valves, there is also a problem in connection with the actuation of the valves. This is particularly true if it is desired to simplify the cylinder head arrangement and only employ a single camshaft for opening at least all of the intake valves. Furthermore, if it is desired to simplify the cylinder head in such a way that only a single camshaft is employed for operating all of the valves, then further problems arise.
It is, therefore, a still further object of this invention to provide an improved multi-valve single overhead camshaft engine.
It is another object of this invention to provide an improved valve arrangement for a single overhead camshaft engine having at least five valves operated by the single camshaft.
When multiple intake valves are employed, there may be certain advantages in having the valve opening areas be different. That is, the effective opening area of the valve is equal to its circumference multiplied by its lift. In some instances it may be desirable to provide valves which have the same diameter of the head but which have different degrees of lift so as to provide desired flow patterns within the cylinder. For example, if one intake valve has a greater effective flow area than others the smaller flow area will tend to cause a higher velocity within the cylinder and can influence the air flow therein. However, when employing an arrangement wherein multiple valves are operated from a single camshaft, than there may be some difficulty in providing different opening and closing characteristics for the valves.
It is, therefore, a still further object of this invention to provide an improved arrangement for varying the valve events of multiple valves operated by a single overhead camshaft.
It is a further object of this invention to provide an arrangement wherein two valves are operated by a common rocker arm and wherein the valves have different lifts but the valves have the same stem length.
When employing multiple intake valves it is possible to provide throttle valve arrangements so that a lesser number of valves serve the engine at low speed operation than high speed operation. Such an arrangement permits the achievement of different flow patterns within the cylinder under different running conditions and, furthermore, can improve combustion efficiency. However, in order to accommodate good low speed running it is desireable to insure that the valve which serves the engine's low speed requirements is served by an intake passage that has a relatively small volume. This insures good response upon opening and closing of the valve. Although it may be possible to provide a low volume by decreasing the cross sectional area of the intake passage, this gives rise to flow restriction. Therefore, it is desireable to maintain a short length for such an intake passage. However, it is not always possible to do this when there are multiple intake passages serving the same cylinder.
It is, therefore, a still further object of this invention to provide an improved induction system for an internal combustion engine having multiple intake valves and wherein the flow passages associated with the valves are optimumly placed.
It is a further object of this invention to provide an improved arrangement for a multiple valve engine wherein effective induction passages are provided for each valve and wherein it is possible to utilize short passages for as many valves as possible.
In staged induction systems, it is also desireable if the intake valves can be operated in such a manner that the intake valve timing and lift is tailored for the running condition for the engine which it serves. However, when multiple intake valves are employed and it is desired to operate them from a single camshaft, this can give rise to additional problems.
It is, therefore, a still further object of this invention to provide an improved valve operating mechanism for a multiple valve engine wherein all valves can be operated by a single camshaft and the timing and lift of one valve may be different from those of the other valves and yet the valves all have the same stem length.